1. Field of the Invention
The present invention relates generally to communication systems, and more particularly to a system and method for improving the pointing accuracy of a transmitter in a communication channel.
2. Related Art
Over the last several years there has been tremendous growth in the deployment of fiber-optic facilities by telecommunications carriers such as Regional Bell Operating Companies (RBOCs), cable carriers, and Competitive Local Exchange Carriers (CLECs). Deployment of these facilities along with the introduction of technologies such as OC-192 and DWDM has dramatically lowered the marginal cost of bandwidth on the fiber.
Thus, as a result of this development, there is extensive bandwidth and communications capability in carriers"" backbone networks. However, many homes and offices do not have a practical solution to interface to these backbone networks. Consequently, direct attachment of potential customers to these backbone networks remains very expensive.
Currently, there are two practical methods for directly attaching customers to backbone networks such as optical fiber networks. These are buried or aerial fiber interconnections and microwave connections. However, both of these methods incur significant up-front costs before any revenue can be realized. In the case of buried or aerial fiber, these costs are associated with obtaining rights-of-way for the cable runs, and installing the cable by burying or hanging. In the case of a microwave system, these up front costs come not only from the cost associated with the microwave repeater equipment, but also from the costs associated with obtaining rights to the suitable portion of the spectrum. Therefore, system developers and integrators have sought long and hard to find suitable solutions to this xe2x80x9clast milexe2x80x9d problem.
The present invention is directed toward a system and method for implementing a communication capability that allows one or more users at one or more user facilities to communicate with a communications network. For example, in one embodiment, the invention allows these users to communicate on one or more backbone networks supported by a common carrier or other service provider. According to one aspect of the invention, a multi-node communication network is provided that interfaces a plurality of buildings, houses, complexes, or other facilities to a service provider""s backbone network. According to one realization, the nodes of the network can be provided with optical transceivers, so that the network links can be implemented as optical communication links. As such, the several buildings integrated by the network can be included in the network without the need to do cabling or otherwise physically connect the facilities. Additionally, the use of optical transceivers avoids the need to be concerned with wireless RF constraints such as bandwidth, interference, FCC approval and restrictions, and other concerns typically associated with RF communication.
According to another aspect of the invention, the nodes of the network can include transceivers that are fixed to a movable mount to facilitate pointing of a transceiver to another node in the network. For example, in one embodiment, an azimuth and elevation mount is provided that allows the transceiver to be pointed with a degree of accuracy to another transceiver in another node in the network.
In addition, one or more controllers can be provided with each node to control the pointing of transceivers and to provide other control features or functions useful in integrating a node within the network. Additionally, the controller can perform routing of data from the node to other nodes in the network and also any communication format changes that may be needed to interface in the network to the backbone network or to interface the network to a user within a facility.
According to another aspect of the invention, an installation fixture can be provided to facilitate the installation and alignment of one or more nodes within the network. Such an installation fixture is particularly useful in embodiments where pointing and alignment are somewhat critical. For example, where the communication links of the network are optical links, such links tend to use a relatively narrow beam width, and low power laser transmitters. As such, with these devices, pointing in alignment is critical to fall within the budgeted link margins.
According to one aspect of the invention, the installation fixture can include automated devices for determining the position of the node as well as the node orientation (e.g., in what direction a point on the fixture is pointing). For example, in one implementation, the installation fixture includes a GPS receiver to determine position information and a digital compass to determine the node orientation. Additionally, the digital compass can also be used to determine roll, pitch and yaw of the device relative to a fixed orientation. Thus, with the roll and pitch parameters, an indication of the level of the installation fixture can also be determined. Where the installation fixture is mounted to a node, determination of parameters for the fixture, results in a determination of these parameters for the node as well. Therefore, the installation fixture, when mounted to a node, can determine location, orientation, and leveling of a node in the network.
These parameters relating to the location and orientation of the node in the network can be used to compute pointing angles to enable the node to communicate with other nodes in the network. In one embodiment, the installation fixture can simply be a data gathering device, which gathers node parameters such as position and orientation information. In this embodiment, the data gathering device provides these parameters to another processor to determine the appropriate pointing angles to allow the transceivers within the node to accurately point to other nodes in the network. This computation can be performed, for example, by a processor within the node, or by a processor or processor-based system at a central office. Alternatively, processing capability can be provided within the installation fixture to enable the installation fixture to determine the pointing angles necessary to interface the subject node with the other nodes in the network. Additionally, processing responsibilities can be shared among the various processors in the system.
In one embodiment, positional information in three dimensions is known for each node in a network. As such, a relatively straight-forward geometric calculation can be used to determine the pointing angles necessary to interface the subject node with other nodes in the network. This positional information can be in terms of x, y, z coordinates relative to the earth. For example, the positional information can be in terms of latitude, longitude, and altitude. Alternative positional coordinates can be used, relative to the earth or relative to another fixed position. Preferably, each node within the network utilizes the same coordinate reference such that pointing angles can be determined without the need to perform additional coordinate translation computations.
According to another aspect of the invention, fine tuning of the transceiver pointing can be performed. In one embodiment, a spatial detector receives a portion of the received data signal. The location at which the beam impinges upon the spatial detector provides an indication of the pointing accuracy. This information can be used to adjust the pointing of the transmitter, for example, to center the beam on the spatial detector. In one realization, to avoid erroneous detection of noise sources, the transmitted data signal is encoded such that it can be identified. In one example, the transmitted data signal is modulated onto a relatively low-frequency carrier. The detector performs its pointing analysis based only on the low-frequency signal. Other signals are ignored. Because most noise sources appear as DC signals, this technique effectively allows the spatial detector to discriminate among the various signals and select the appropriate one.
According to another aspect of the invention, a technique for controlling the effective power of the beam carrying the data signal is provided. Because a range of atmospheric and other conditions can lead to a large range in received power, it is conceivable that the received beam can be outside the dynamic range of the receiver. For example, where the transmitter is adjusted to provide adequate power in fog or other adverse weather conditions, the transmitter may be overpowered in ideal weather conditions. This can result in saturation of the detector.
Therefore, in one embodiment, the signal strength of the received signal is measured, and it is determined whether the power needs to be adjusted. If so, the transmitter is directed to adjust its pointing such that the effective power impinging on the remote detector is adjusted. For example, where the power exceeds a determined threshold level, the transmitter may be directed to look-off from the on-center pointing, to decrease the signal level of the beam impinging upon the remote detector. As such, the effective power is decreased to that which is within the dynamic range of the receiver. In one embodiment, this direction can be provided via a control channel on the link.
Further features and advantages of the invention as well as the structure and operation of various embodiments of the invention are described in detail below with reference to the accompanying drawings.